Sometimes referred to as "glue," an adhesive is a substance used to bond together two surfaces and is generally sticky in texture. Structural adhesives for automotive assembly are engineered to form bonds that can support loads (via load-bearing joints) and are formulated to improve manufacturing processes and final products for a variety of composite, metal and plastic assemblies. To learn more about how automotive assembly adhesives work, advantages of using structural adhesives, types of structural adhesives (acrylic, epoxy and urethane) and best practices for the application and testing of structural adhesives, please read the sections below.
Basics of Adhesion
As the term implies, adhesives work through the process of adhesion. There are two important factors to understand the basics of adhesion:
- Wetting - The ability of an adhesive to maintain intimate contact with the surfaces to be bonded. Adhesives rely heavily on good wetting to achieve maximum adhesion. In the figure seen to the right, substance "A" has virtually no wetting (very poor to no adhesion), substance "B" has low wetting (poor adhesion), and substance "C" has high wetting (strong adhesion).
- Method of Adhesion:
- Chemical - The adhesive and substrate form chemical bonds:
- Mechanical - The adhesive fills imperfections (voids, pores, scratches, etc.) in the substrate surface:
- Diffusion or Adsorption - The adhesive diffuses into the substrate at the molecular level: